3.3.8 - Aldehydes And Ketones
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Aldehydes end in … And give example
• Anal Eg pentanal
Ketones end in … Give example ..
-one Eg propanone
What is carbonyl group
C=O
Can ketones be oxidesued
No
Aldehydes can be readily oxidised to ..
Carboxylic acids
Propanal oxidised to…
Propanoic acid
How to distinguish between aldehyde and ketone (2 ways)
Tollens reagent Fehlings solution
+ve result for aldehyde using tollens
Silver mirror
-ve test result for ketone using tollens
No visible change
What colour is fehlings solution and whag is it
Blue solution of copper (ll) ions Dissolves in NaOH
+ve test result for aldehydes using fehlings solution
Brick red ppt Of copper (l) oxide
A primary alchol can be oxidised into a …. And then to a …
1• alcohol —-> aldehyde —> carboxylic acid
Secondary alcohol can be oxidised into a …
Ketone
Aldehydes can be reduced into ..
Primary alchol
Ketones can be reduced into …
Secondary Alcohol
What is the reducing agent
NaBH4
CN can react with carbonyls to undergo nucleophillic addition via
Reacting w KCN or HCN
How to draw cyanide ion
• :CN Lone pair … minus sign must be on top of carbon
Aldehydes and unsymmetric ketones form mixtures of _____ When reacted with KCN followed by a dilute acid
Enantiomers
Hazards of using KCN
• is an irritant, dangerous if digested or inhaled • toxic and poisonous
why is KCN used instead of HCN
HCN is weak
General equation for reacting aldehyde with KCN
H+(aq) RCHO(aq) + KCN(aq) —> RCH(OH)CN(aq) + K^+ (aq)
Equation for overall reaction between ketone and KCN
H+(aq) RCOR’ (aq) + KCN (aq) —> RCR’(OH)CN (aq) + K+(aq)
why does NaBH4 reduced butanal but not butene
3 H– ion / nucleophile is attracted to δ+ C 1 M4 electron rich C=C 1 M5 H– ion / nucleophile is repelled by C=C OR C=C only attacked by/reacts with electrophiles